Process for the production of jet-range hydrocarbons

ABSTRACT

A method for producing jet-range hydrocarbons includes passing a renewable olefin feedstock comprising C 3  to C 8  olefins to an oligomerization reactor containing a zeolite catalyst to produce an oligomerized effluent, separating the oligomerized effluent into at least a C 7 − hydrocarbon stream, a heavy olefin stream, and a jet range olefin stream. At least a portion of the heavy olefin stream is recycled to the oligomerization reactor to dilute the renewable C 4  olefin feedstock. The jet range olefin stream may be hydrotreated and separated to provide a jet range hydrocarbon product.

FIELD OF THE INVENTION

The present disclosure generally relates to methods for producingrenewable fuels and chemicals from biorenewable sources and therenewable fuels and chemicals produced thereby, and more particularlyrelates to methods for producing jet-range hydrocarbons from alkanols,including for example isobutanol.

BACKGROUND OF THE INVENTION

As the worldwide demand for fuel increases, interest in sources otherthan crude oil from which to produce transportation fuels, includingaviation fuels, is ever increasing. For example, due to the growingenvironmental concerns over fossil fuel extraction and economic concernsover exhausting fossil fuel deposits, there is a demand for using analternate or “green” feed source for producing hydrocarbons for use astransportation fuels and for use in other industries. Such sources ofinterest include, for example, biorenewable sources, such as vegetableand seed oils, animal fats, and algae byproducts, among others as arewell-known to those skilled in the art. A conventional catalytichydro-processing technique is known for converting a biorenewablefeedstock into green diesel fuel that may be used as a substitute forthe diesel fuel produced from crude oil. As used herein, the terms“green diesel fuel” and “green jet fuel” refer to fuel produced frombiorenewable sources, in contrast to those produced from crude oil. Theprocess also supports the possible co-production of propane and otherlight hydrocarbons, as well as naphtha or green jet fuel.

Biomass fermentation products typically include lower isoalkanols suchas, for example, C₃ to C₈ isoalkanols obtained by contacting biomasswith biocatalysts that facilitate conversion (by fermentation) of thebiomass to isoalkanols of interest. The biomass feedstock for suchfermentation processes can be any suitable fermentable feedstock knownin the art, such as fermentable sugars derived from agricultural cropsincluding sugarcane, corn, etc. Suitable fermentable biomass feedstockcan also be prepared by the hydrolysis of biomass, for examplelignocellulosic biomass (e.g. wood, corn stover, switchgrass, herbiageplants, ocean biomass, etc.), to form fermentable sugars.

Jet-range fuels are an important product for the aerospace industry andthe military. The specific characteristics of various grades and typesof jet-range fuels vary slightly according to the particular applicationand environment in which they are used. Generally, jet-range fuelscomprise a mixture of primarily C₈ to C₁₆ hydrocarbons and typicallyhave a freezing point of about −40 or −47° C. (−40 or −52.6° F.). Inorder to produce jet-range fuels from isoalkanols derived from fermentedbiomass, in one example known in the art, isobutanol is first dehydratedto form butenes. The butenes are then oligomerized, in the presence ofan oligomerization catalyst, in one or more reactors to form heavierolefins, such as C₅ to C₂₀, or even higher, olefinic oligomers. Finally,the resulting olefinic oligomers are hydrogenated in a saturationreactor to form the corresponding C₅ to C₂₀, or even higher, paraffinsin a mixture which can then be subjected to separation to obtain C₉ toC₂₀₊ paraffins suitable for use as biorenewable jet fuel.

Since the oligomerization reaction is highly exothermic, the butene fedto the oligomerization reactors may be cooled before entering theoligomerization reactors. Another measure taken to control thetemperature increase in the oligomerization reactors is to limit theproportion of olefins contained in the feed stream provided to eachreactor to no more than about 15 percent by weight (wt %). This isaccomplished, at least in part, by adding non-reactive diluent materialto the reactors which also provides a heat sink to control thetemperature rise in the reactors.

Typically, this dilution may be done by recycling saturated distillateproduct from a stripped effluent of a hydrogenation section back to theoligomerization and hydrogenation reactors. Hydrogen transfer from thesaturated diluent to the light olefinic feed to the oligomerizationreactor can cause yield loss by saturating the light olefin feeds intoparaffins. Paraffins, however, will not participate in theoligomerization reactions and will be recovered as saturated liquefiedpetroleum gas, instead of olefinic distillate range material. Since thedesired product is a distillate range material, conversion of theolefins into saturated liquefied petroleum gas amounts to a loss ofpotential distillate yield, and thus is considered undesirable.

Therefore, it would be desirable to have one or more processes in whichthe dilution of the feedstock to the oligomerization reactor is lesslikely to result in yield loss.

SUMMARY OF THE INVENTION

One or more processes have been invented in which a portion of an olefineffluent from an oligomerization reaction is used to dilute a feedstockto the oligomerization reaction.

In a first aspect of the invention, the present invention may be broadlycharacterized as providing a process for producing jet rangehydrocarbons by: oligomerizing a renewable olefin feedstock comprisingC₃ to C₈ olefins in an oligomerization reactor containing a catalyst andbeing operated under conditions to produce an oligomerized effluent;separating the oligomerized effluent to produce a light hydrocarbonstream, a naphtha olefin hydrocarbon stream, and a heavy streamcomprising C₈₊ olefins; separating the heavy stream into a jet rangeolefin stream and an olefin recycle stream comprising diesel rangeolefins; and, diluting the renewable olefin feedstock with at least aportion of the olefin recycle stream.

In one or more embodiments of the present invention, the process furthercomprises blending a portion of the olefin recycle stream in a dieselblending pool. It is contemplated that the process includeshydrogenating the portion of the olefin recycle stream blended in thediesel blending pool before blending.

In various embodiments of the present invention, the process furthercomprises recycling at least a portion of the naphtha olefin hydrocarbonstream to the oligomerization reactor.

In some embodiments of the present invention, the process furthercomprises hydrogenating the jet range olefin stream in a hydrogenationzone having a hydrogenating reactor to provide a hydrogenated effluent.It is contemplated that the process includes separating the hydrogenatedeffluent into a vent gas stream and a jet range hydrocarbons stream. Itis also contemplated that the process includes recycling at least aportion of the jet range hydrocarbons stream to the hydrogenation zone.

In a second aspect of the present invention, the present invention maybe generally characterized as providing a process for producing jetrange hydrocarbons by: passing a renewable olefin feedstock comprisingC₃ to C₈ olefins to an oligomerization reaction zone comprising anoligomerization reactor containing a catalyst and being operated underconditions to produce an oligomerized effluent; passing the oligomerizedeffluent to a first separation zone to provide at least one streamcomprising C⁷⁻ hydrocarbons, a diesel range olefin recycle stream, and ajet range olefin stream; and, recycling at least a first portion of thediesel range olefin recycle stream to the oligomerization reaction zone.

In at least one embodiment of the present invention, the process furthercomprises combining the first portion of the diesel range olefin recyclestream with the renewable olefin feedstock to provide a combined streamand passing the combined stream into the oligomerization reactor.

In one or more embodiments of the present invention, the process furthercomprises passing a second portion of the diesel range olefin recyclestream to a diesel blending pool. It is contemplated that the processincludes hydrogenating the second portion of the diesel range olefinrecycle stream before it is passed to the diesel blending pool.

In various embodiments of the present invention, the first separationzone produces a light hydrocarbon stream and a naphtha olefinhydrocarbon stream. It is contemplated that the first separation zonecomprises two fractionation columns. It is also contemplated that thefirst fractionation column provides the light hydrocarbon stream and thenaphtha olefin hydrocarbon stream, and that the second fractionationcolumn provides the diesel range olefin recycle stream and the jet rangeolefin stream. It is further contemplated that the process includespassing at least a portion of the naphtha hydrocarbon stream to theoligomerization reactor.

In one or more of the embodiments of the present invention, the processfurther comprises passing the jet range olefin stream to a hydrogenationzone having a hydrogenating reactor containing a catalyst and beingoperated to provide a hydrogenated effluent. It is contemplated that theprocess includes passing the hydrogenated effluent to second separationzone to provide a vent gas stream and a jet range hydrocarbons stream.It is contemplated that the process also includes passing at least aportion of the jet range hydrocarbons stream to the hydrogenatingreaction zone as a recycle jet range stream. It is contemplated that theprocess further includes combining the recycle jet range stream and thejet range olefin stream in a jet range combined stream and passing thejet range combined stream to the hydrogenating reactor.

In at least one of the embodiments of the present invention, the firstseparation zone comprises at least two fractionation columns arranged inseries.

Additional aspects, embodiments, and details of the invention, which maybe combined in any manner, are set forth in the following detaileddescription of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

One or more exemplary embodiments of the present invention will bedescribed below in conjunction with the following drawing FIGURE, inwhich:

the FIGURE shows a process flow diagram of one or more processesaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “stream” can include various hydrocarbonmolecules and other substances. Moreover, the term “stream comprisingC_(x) hydrocarbons” or “stream comprising C_(x) olefins” can include astream comprising hydrocarbon or olefin molecules, respectively, with“x” number of carbon atoms, suitably a stream with a majority ofhydrocarbons or olefins, respectively, with “x” number of carbon atomsand preferably a stream with at least 75 wt % hydrocarbons or olefinmolecules, respectively, with “x” number of carbon atoms. Moreover, theterm “stream comprising C_(x)+ hydrocarbons” or “stream comprisingC_(x)+ olefins” can include a stream comprising a majority ofhydrocarbon or olefin molecules, respectively, with more than or equalto “x” carbon atoms and suitably less than 10 wt % and preferably lessthan 1 wt % hydrocarbon or olefin molecules, respectively, with x−1carbon atoms. Lastly, the term “C_(x)− stream” can include a streamcomprising a majority of hydrocarbon or olefin molecules, respectively,with less than or equal to “x” carbon atoms and suitably less than 10 wt% and preferably less than 1 wt % hydrocarbon or olefin molecules,respectively, with x+1 carbon atoms.

As used herein, the term “zone” can refer to an area including one ormore equipment items and/or one or more sub-zones. Equipment items caninclude one or more reactors or reactor vessels, heaters, exchangers,pipes, pumps, compressors, controllers and columns. Additionally, anequipment item, such as a reactor, dryer, or vessel, can further includeone or more zones or sub-zones.

As used herein, the term “substantially” can mean an amount of at leastgenerally about 70%, preferably about 80%, and optimally about 90%, byweight, of a compound or class of compounds in a stream.

As used herein, the term “gasoline” can include hydrocarbons having aboiling point temperature in the range of about 25 to about 200° C. (68to 392° F.) at atmospheric pressure.

As used herein the term “naphtha” can mean C₅ hydrocarbons up tohydrocarbons having a boiling point of 150° C. (302° F.) (i.e.,hydrocarbons having a boiling point in the range of 30 to 150° C. (86 to302° F.)).

As used herein the term “diesel” can include hydrocarbons having aboiling point temperature in the range of about 250 to about 400° C.(482 to 752° F.) at atmospheric pressure.

As used herein the term “jet-range hydrocarbons,” “jet-range paraffins,”“jet-range fuels,” or “jet fuels” can include hydrocarbons having aboiling point temperature in the range of about 130 to about 300° C.(266 to 572° F.), preferably 150 to 260° C. (302 to 500° F.), atatmospheric pressure. Additionally, as used herein, the terms “jet-rangehydrocarbons,” “jet-range paraffins,” “jet-range fuels,” or “jet fuels”refer to a mixture of primarily C₈ to C₁₆ hydrocarbons with a freezingpoint of about −40° C. (−40° F.) or about −47° C. (−52.6° F.).

As used herein, the term “distillate” comprises a mixture of diesel andjet-range hydrocarbons and can include hydrocarbons having a boilingpoint temperature in the range of about 150 to about 400° C. (302 to752° F.) at atmospheric pressure.

As used herein, the phrase “a mixture of primarily . . . ” or“comprising primarily . . . ” a specified range of carbon-numberedhydrocarbons means that the group or category of hydrocarbons beingdescribed may also contain very small amounts of hydrocarbons outsidethe stated carbon number range, without altering the generalcharacteristics (e.g., boiling point) of the group or category beingdescribed. For example, the description that jet fuels are a mixture ofprimarily C₈ to C₁₆ hydrocarbons means that jet fuels contain at least80 wt % of hydrocarbon molecules each having from about 8 to about 16carbon atoms with, possibly, very small amounts of hydrocarbon moleculeseach having less than about 8 carbon atoms, as well as very smallamounts of hydrocarbon molecules each having more than 16 carbon atoms,such that the freezing point remains about −40° C. to about −47° C. (−40to 52.6° F.). There are multiple standards, established by variousindustries and governments, that are useful for ensuring that particulartypes of jet fuels have uniform characteristics that fall withinexpected ranges. For example, one type of jet fuel, known as AviationTurbine Fuel, Jet A, or Jet A-1 fuel, is composition of hydrocarbonsthat boil in a range such that the volatility characteristics of thehydrocarbon (or paraffinic form of the hydrocarbon after hydrogenation)substantially conform to the volatility standards of flash point(typically minimum of 38° C. (100° F.), distillation range (T10 boilingpoint maximum of 205° C. (401° F.) and final boiling point (maximum of300° C. (572° F.), with all distillation valves measured by D86 or D2887values converted to D86) set forth in ASTM D7566-11a, “StandardSpecification for Aviation Turbine Fuel Containing SynthesizedHydrocarbons,” promulgated by ASTM International, Inc. of WestConshohoken, Pa. Other standards that provide parameters useful forcharacterizing and defining the jet fuels prepared using the methods andapparatus contemplated and described herein include Jet Propellant(JP)-5 and JP-8, which are set forth in the United States militaryspecifications found at MIL-DTL-83133, as well as in British DefenceStandard 91-87.

The term “column” means a distillation column or columns for separatingone or more components of different volatilities. Unless otherwiseindicated, each column includes a condenser on an overhead of the columnto condense and reflux a portion of an overhead stream back to the topof the column and a reboiler at a bottom of the column to vaporize andsend a portion of a bottom stream back to the bottom of the column.Feeds to the columns may be preheated. The top pressure is the pressureof the overhead vapor at the outlet of the column. The bottomtemperature is the liquid bottom outlet temperature. Overhead lines andbottom lines refer to the net lines from the column downstream of thereflux or reboil to the column.

As used herein, the term “boiling point temperature” means atmosphericequivalent boiling point (AEBP) as calculated from the observed boilingtemperature and the distillation pressure, as calculated using theequations furnished in ASTM D1160 appendix A7 entitled “Practice forConverting Observed Vapor Temperatures to Atmospheric EquivalentTemperatures.”

As used herein, “taking a stream from” means that some or all of theoriginal stream is taken.

As mentioned above, one or more methods have been invented for producingjet-range hydrocarbons from one or more biorenewable C₃ to C₈ olefinsvia oligomerization. The oligomerization reaction is highly exothermicand in order to control the temperature rise from the inlet to theoutlet of the reactor (i.e., ΔT), various processes utilize a diluent.However, it has been discovered that by using a portion of the heavyolefins produced in the oligomerization reactor, the temperature risecan be controlled without using paraffins which may transfer hydrogensto the olefins in the oligomerization reactor to saturate the smallerolefins. The heavy olefins have been found to resist furtheroligomerization, resulting in a diluent that can minimize yield loss.While these methods find greatest utility in converting feedstocks fromalkanols, thereby allowing for production of jet fuels from renewablesources, this is not intended to limit the application of the methods ofthe present invention.

With these general principles in mind, one or more embodiments of thepresent invention will be described with the understanding that thefollowing description is not intended to be limiting.

As shown in the FIGURE, one or more processes of the present inventioninclude a renewable olefin feedstock 10 being passed to anoligomerization zone 12. As used herein, the term “renewable” denotesthat the carbon content of the olefin feedstock 10 is from a “newcarbon” source as measured by ASTM test method D6866-05, “Determiningthe Bio-based Content of Natural Range Materials Using Radiocarbon andIsotope Ratio Mass Spectrometry Analysis”, incorporated herein byreference in its entirety. This test method measures the ¹⁴C/¹²C isotoperatio in a sample and compares it to the ¹⁴C/¹²C isotope ratio in astandard 100% bio-based material to give percent bio-based content ofthe sample. Additionally, “bio-based materials” are organic materials inwhich the carbon comes from recently (on the order of centuries) fixatedcarbon dioxide present in the atmosphere using sunlight energy(photosynthesis). On land, this carbon dioxide is captured or fixated byplant life (e.g., agricultural crops or forestry materials). In theoceans, the carbon dioxide is captured or fixated by photosynthesizingbacteria or phytoplankton. For example, a bio-based material has a¹⁴C/¹²C isotope ratio greater than zero. Contrarily, a fossil-basedmaterial has a ¹⁴C/¹²C isotope ratio of zero. The term “renewable” withregard to compounds such as alcohols or hydrocarbons (olefins,di-olefins, polymers, etc.) also refers to compounds prepared frombiomass using thermochemical methods (e.g., Fischer-Tropsch catalysts),biocatalysts (e.g., fermentation), or other processes, for example asdescribed herein.

A small amount of the carbon atoms in the carbon dioxide in theatmosphere is the radioactive isotope ¹⁴C. This ¹⁴C carbon dioxide iscreated when atmospheric nitrogen is struck by a cosmic ray generatedneutron, causing the nitrogen to lose a proton and form carbon of atomicmass 14 (¹⁴C), which is then immediately oxidized, to carbon dioxide. Asmall but measurable fraction of atmospheric carbon is present in theform of ¹⁴C.

Atmospheric carbon dioxide is processed by green plants to make organicmolecules during the process known as photosynthesis. Virtually allforms of life on Earth depend on this green plant production of organicmolecules to produce the chemical energy that facilitates growth andreproduction. Therefore, the ¹⁴C that forms in the atmosphere eventuallybecomes part of all life forms and their biological products, enrichingbiomass and organisms which feed on biomass with ¹⁴C. In contrast,carbon from fossil fuels does not have the signature ¹⁴C/¹²C ratio ofrenewable organic molecules derived from atmospheric carbon dioxide.Furthermore, renewable organic molecules that biodegrade to carbondioxide do not contribute to an increase in atmospheric greenhouse gasesas there is no net increase of carbon emitted to the atmosphere.Assessment of the renewably based carbon content of a material can beperformed through standard test methods, e.g. using radiocarbon andisotope ratio mass spectrometry analysis. ASTM International (formallyknown as the American Society for Testing and Materials) has establisheda standard method for assessing the bio-based content of materials. TheASTM method is designated ASTM-D6866. The application of ASTM-D6866 toderive “bio-based materials” is built on the same concepts asradiocarbon dating, but without use of the age equations. The analysisis performed by deriving a ratio of the amount of radiocarbon (¹⁴C) inan unknown sample compared to that of a modern reference standard. Thisratio is reported as a percentage with the units “pMC” (percent moderncarbon). If the material being analyzed is a mixture of present dayradiocarbon and fossil carbon (containing very low levels ofradiocarbon), then the pMC value obtained correlates directly to theamount of biomass material present in the sample. In an aspect,renewable carbon substantially comprises the feedstock. The percentageof renewable carbon in the feedstock may be greater than 80% or greaterthan 90% or greater than 95% or greater than 99% on a weight basis.

Returning to the FIGURE, the renewable olefin feedstock 10 includes atleast C₄ olefins and preferably comprising C₃ to C₈ olefins. In anaspect, the renewable olefin stream may comprise one or more carbonnumber olefins such as C₃ to C₄ olefins or C₃ to C₅ olefins or C₄ to C₅olefins or C₃ to C₆ olefins. The renewable olefins may be derived fromtheir corresponding alcohols (i.e., C₄ alcohols, especially includingisobutanol), which are typically formed by fermentation or bycondensation reactions of synthesis gas. For example, a feedstock forthe fermentation process can be any suitable fermentable feedstock knownin the art, such as sugars derived from agricultural crops includingsugarcane, corn, etc. Alternatively, the fermentable feedstock can beprepared by the hydrolysis of biomass, for example lignocellulosicbiomass (e.g. wood, corn stover, switchgrass, herbiage plants, oceanbiomass, etc.). In another example, renewable alcohols, such asisobutanols, can be prepared photosynthetically, for example usingcyanobacteria or algae engineered to produce isobutanol and/or otheralcohols. When produced photosynthetically, the feedstock for producingthe resulting renewable alcohols is light, water, and carbon dioxide,which is provided to the photosynthetic organism (e.g., cyanobacteria oralgae). Additionally, other known methods, whether biorenewable orotherwise, for producing isobutanol are suitable for supplying the C₄olefins; the methods described herein are not intended to be limited bythe use of any particular renewable feed source.

Typically, the renewable olefin feedstock 10 may comprise greater than50 wt % olefins such as greater than 70 wt % or greater than 80 wt % orgreater than 90 wt % olefins or greater than 95 wt % or greater than 99wt % olefins.

Olefin isomer types of the renewable olefin stream and of the oligomersproduced by oligomerization can be denominated according to the degreeof substitution of the double bond, as follows:

TABLE 1 Olefin Type Structure Description I R—HC═CH₂ Monosubstituted IIR—HC═CH—R Disubstituted III RRC═CH₂ Disubstituted IV RRC═CHRTrisubstituted V RRC═CRR Tetrasubstitutedwherein R represents an alkyl group, each R being the same or different.Type I compounds are sometimes described as α- or vinyl olefins and TypeIII as vinylidene olefins. Type IV is sometimes subdivided to provide aType IVA, in which access to the double bond is less hindered, and TypeIVB where it is more hindered. In an aspect, the renewable olefinfeedstock 10 may comprise high quantities of Type III olefins such asgreater than 50 wt % or greater than 70 wt % or greater than 85 wt % orgreater than 90 wt % or greater than 95 wt % Type III olefins as afraction of the total olefins in the renewable olefins feedstock 10.

The renewable olefins (possibly derived and converted from the C₄alcohols, for example by dehydration of the alcohol, see, e.g., U.S.Pat. No. 4,423,251) in the renewable feedstock 10 are mixed with adiluent stream 14 (discussed in more detail below) to form a combinedstream 16 which is passed to an oligomerization reactor 18 in theoligomerization zone 12. Although depicted with a single oligomerizationreactor 18, the oligomerization zone 12 may contain any number ofreactors.

In the oligomerization reactor 18, at least a portion of the renewableolefins are converted into a mixture of heavier boiling hydrocarbonsincluding jet range hydrocarbons via oligomerization by reacting theolefins using a zeolitic oligomerization catalyst under appropriateconditions. For example, the oligomerization zone 12 may, for example,without limitation, be operated at a temperature from about 100 to about300° C. (212 to 572° F.) and a pressure of from about 689 to about 6895kPa (100 to 1000 psig). For example, the operating temperature may befrom about 120 to about 280° C. (248 to 536° F.), or even from about 160to about 260° C. (320 to 402.8° F.). The operating pressure may, forexample, be from about 1034 to about 5516 kPa (150 to 800 psi), or evenfrom about 2068 to about 4964 kPa (300 to 720 psi).

The oligomerization catalyst in the oligomerization zone 12 is notlimited to any particular catalyst and may comprise any catalystsuitable for catalyzing conversion of the one or more biorenewable C₃ toC₈ olefins in the olefin stream to olefinic oligomers comprising heavierboiling C₅₊ hydrocarbons, including jet-range hydrocarbons. Theoligomerization catalyst may be any such catalyst known now or in thefuture.

Conventional oligomerization catalysts will generally convert an olefinto a mixture of dimers, trimers, tetramers, and sometimes pentamers, ofthe olefin. For example, where the C₃ to C₈ olefin is isobutylene, a C₄olefin, the products of oligomerization in the presence of aconventional oligomerization catalyst include C₈, C₁₂, C₁₆, andsometimes C₂₀ olefins, together in a mixture. Conventionaloligomerization catalysts include, without limitation, solid phosphoricacid (“SPA”) and certain ion exchange resins such as Amberlyst-36(commercially available from The Dow Chemical Company of Midland, Mich.,U.S.A.). The olefinic oligomer mixture produced using conventionaloligomerization catalysts may be further subjected to a separationprocess to produce a mixture of jet-range hydrocarbons suitable for useas jet fuels. These jet fuels often have a boiling point distributionthat has well-defined boiling point steps corresponding to only a fewisomers of the corresponding trimer, tetramer, and pentamer paraffins ofthe starting olefin, which is different from petroleum-derived jetfuels.

Alternative oligomerization catalysts comprising zeolite materials, onthe other hand, catalyze oligomerization conversion of C₃ to C₈ olefinsto dimers, trimers, tetramers, and sometimes pentamers of the C₃ to C₈olefins, but also catalyze backcracking conversion of the resultingheavier olefinic oligomers back into lighter and more random and variedsizes of olefins including C₅ to C₂₀₊ hydrocarbons. In other words,under appropriate conditions, zeolitic catalysts such as, withoutlimitation, MTT, TON, MFI, and MTW, yield C₅₊ hydrocarbons, includingjet-range hydrocarbons, with an increased distribution and variety ofcarbon numbers than those made using conventional non-zeoliticcatalysts. This means that jet-range fuel produced from biorenewableolefins via oligomerization in the presence of zeolite catalysts has aboiling range and compositional profile that is more similar tojet-range fuels produced from petroleum refining processes.

Suitable zeolite catalysts may comprise between 5 and 95 wt % of zeolitematerial. Suitable zeolite materials include zeolites having a structurefrom one of the following classes: MFI, MEL, ITH, IMF, TUN, FER, BEA,FAU, BPH, MEI, MSE, MWW, UZM-8, MOR, OFF, MTW, TON, MTT, AFO, ATO, andAEL. 3-letter codes indicating a zeotype are as defined by the StructureCommission of the International Zeolite Association and are maintainedat http://www.iza-structure.org/databases/. UZM-8 is as described inU.S. Pat. No. 6,756,030. In a preferred aspect, the zeolite catalyst maycomprise a zeolite with a framework having a ten-ring pore structure.Examples of suitable zeolites having a ten-ring pore structure includeTON, MTT, MFI, MEL, AFO, AEL, EUO and FER. The oligomerization catalystcomprising a zeolite having a ten-ring pore structure may comprise auni-dimensional pore structure. A uni-dimensional pore structureindicates zeolite materials containing non-intersecting pores that aresubstantially parallel to one of the axes of the crystal. The porespreferably extend through the zeolite crystal. Suitable examples ofzeolite materials having a ten-ring uni-dimensional pore structure mayinclude MTT. In a further aspect, the oligomerization catalyst comprisesan MTT zeolite.

The zeolite catalyst may be formed by combining the zeolite materialwith a binder, and then forming the catalyst into pellets. The pelletsmay optionally be treated with a phosphorus reagent to create a zeolitehaving a phosphorous component between 0.5 and 15 wt % of the treatedcatalyst. The binder is used to confer hardness and strength on thecatalyst. Binders include alumina, aluminum phosphate, silica,silica-alumina, zirconia, titania and combinations of these metaloxides, and other refractory oxides, and clays such as montmorillonite,kaolin, palygorskite, smectite and attapulgite. A preferred binder is analuminum-based binder, such as alumina, aluminum phosphate,silica-alumina and clays.

One of the components of the zeolite catalyst binder utilized herein isalumina. The alumina source may be any of the various hydrous aluminumoxides or alumina gels such as alpha-alumina monohydrate of the boehmiteor pseudo-boehmite structure, alpha-alumina trihydrate of the gibbsitestructure, beta-alumina trihydrate of the bayerite structure, and thelike. A suitable alumina is available from UOP LLC under the trademarkVersal. A preferred alumina is available from Sasol North AmericaAlumina Product Group under the trademark Catapal. This material is anextremely high purity alpha-alumina monohydrate (pseudo-boehmite) whichafter calcination at a high temperature has been shown to yield a highpurity gamma-alumina.

A suitable zeolite catalyst may be, for example, prepared by mixingproportionate volumes of zeolite and alumina to achieve the desiredzeolite-to-alumina ratio. In an embodiment, the MTT content may be about5 to 85 wt %, for example about 20 to 82 wt % MTT zeolite, and thebalance alumina powder will provide a suitably supported catalyst. Asilica support is also contemplated.

Monoprotic acid such as nitric acid or formic acid may be added to themixture in aqueous solution to peptize the alumina in the binder.Additional water may be added to the mixture to provide sufficientwetness to constitute a dough with sufficient consistency to be extrudedor spray dried. Extrusion aids such as cellulose ether powders can alsobe added. A preferred extrusion aid is available from The Dow ChemicalCompany under the trademark Methocel.

The paste or dough may be prepared in the form of shaped particulates,with the preferred method being to extrude the dough through a diehaving openings therein of desired size and shape, after which theextruded matter is broken into extrudates of desired length and dried. Afurther step of calcination may be employed to give added strength tothe extrudate. Generally, calcination is conducted in a stream of air ata temperature from about 260 to about 815° C. (500 to 1500° F.). The MTTcatalyst is not selectivated to neutralize acid sites such as with anamine.

The extruded particles may have any suitable cross-sectional shape,i.e., symmetrical or asymmetrical, but most often have a symmetricalcross-sectional shape, preferably a spherical, cylindrical or polylobalshape. The cross-sectional diameter of the particles may be as small as40 μm; however, it is usually about 0.635 mm (0.25 inch) to about 12.7mm (0.5 inch), preferably about 0.79 mm ( 1/32 inch) to about 6.35 mm(0.25 inch), and most preferably about 0.06 mm ( 1/24 inch) to about4.23 mm (⅙ inch).

Returning to the FIGURE, an oligomerized effluent 20 from theoligomerization zone 12 may be passed to a separation zone 22 which mayinclude one or more distillation columns 24 a, 24 b. In the separationzone 22, the oligomerized effluent 20 may be separated into at least onestream comprising C⁷⁻ hydrocarbons 26 a, 26 b, an olefin recycle stream28, and a jet range olefin stream 30. In a preferred embodiment, the atleast one stream comprising C⁷⁻ hydrocarbons 26 a, 26 b is two streams,a light hydrocarbon stream 26 a comprising C⁴⁻ hydrocarbons, and anaphtha olefin hydrocarbon stream 26 b comprising C₅ to C₇ hydrocarbons.As will be appreciated, there may be some overlap between the componentsof the various streams. For example, the naphtha olefin hydrocarbonstream 26 b may include some C₄ hydrocarbons or some heavierhydrocarbons such as C₈ or C₉ hydrocarbons. It is preferred that suchstreams include at least 50% of the intended components, (i.e., thenaphtha olefin hydrocarbon stream 26 b comprises 80% C₅ to C₇hydrocarbons).

In a preferred embodiment, a first distillation column 24 a separatesthe oligomerized effluent 20 into the light hydrocarbon stream 26 a, thenaphtha olefin hydrocarbon stream 26 b and a heavy hydrocarbon stream 32comprising mostly C₈₊ olefins such as distillate. In some embodiments ofthe present invention, the naphtha olefin hydrocarbon stream 26 b may berecycled to the oligomerization zone 12 to increase the yield of jetrange olefins that are produced (the optional recycling of the naphthaolefin hydrocarbon stream 26 b is shown as a dashed line in the FIGURE).The further processing of the light hydrocarbon stream 26 a is notnecessary for an understanding or practicing of the present invention.

The heavy hydrocarbon stream 32 is passed to a second distillationcolumn 24 b which will separate the components of the heavy hydrocarbonstream 32 into the olefin recycle stream 28 comprising diesel rangeolefins and the jet range olefin stream 30. The further processing ofthe jet range olefin stream 30 is described below. The olefin recyclestream 28, or at least a portion 28 b thereof, is used to dilute therenewable olefin feedstock 10 as the diluent stream 14. A second portion28 a of the olefin recycle stream 28 may also be withdrawn from theprocess, and passed, for example, to a diesel blending pool as an olefincomponent for diesel fuel. It is contemplated that the second portion 28a of the olefin recycle stream 28 may be hydrogenated in a hydrogenationzone (not shown) to increase the paraffins prior to blending as acomponent for diesel fuel. Exemplary conditions for a hydrogenation zoneare discussed below.

The heavy olefins in the olefin recycle stream 28 are relatively inertin the oligomerization reactor 18 and have a low tendency to furtherreact with the smaller olefins in the oligomerization reactor 18. Thus,the use of the heavy olefins to control the temperature in theoligomerization reactor 18 is desirable because the heavy olefins areless likely to transfer hydrogens to the smaller olefins resulting inyield loss. It is contemplated that the amount of the first portion 28 bof the olefin recycle stream 28 that is used as a diluent is adjustedbased upon the amount C₈₊ olefins produced, as well as the temperatureand temperature rise in the oligomerization reactor 18. If thetemperature or temperate rise is too high, more of the olefin recyclestream 28 may be used as a diluent (i.e., second portion 28 b of theolefin recycle stream 28 increases). Over time, the amount of olefinrecycle stream 28 may build up, requiring the withdrawn portion 28 a tobe increased to control the amount of the olefin recycle stream 28.Across a single bed of oligomerization catalyst, the exothermic reactionwill cause the temperature to rise. Consequently, the oligomerizationreactor 18 should be operated to allow the temperature at the outlet tobe over about 25° C. greater but no more than 60° C. greater than thetemperature at the inlet. In some embodiments, this temperaturedifference between the outlet and the inlet of the oligomerizationreactor 18, the ΔT, is at least 25° C. but no more than 40° C. In stillother embodiments, the ΔT is at least 25° C. but no more than 35° C.

Returning to the FIGURE, the jet range olefin stream 30, along with ahydrogen containing gas 34 may be passed to a hydrogenation zone 36having a hydrogenation reactor 38. In the hydrogenation reactor 38,hydrogenation may be performed using a conventional hydrogenation orhydrotreating catalyst, which may include metallic catalysts containing,e.g., palladium, rhodium, nickel, ruthenium, platinum, rhenium, cobalt,molybdenum, or combinations thereof, and the supported versions thereof.Catalyst supports can be any solid, inert substance including, but notlimited to, oxides such as silica, alumina, titania, calcium carbonate,barium sulfate, and carbons. The catalyst support can be in the form ofpowder, granules, pellets, or the like. Hydrogenation suitably occurs ata temperature of about 150° C. (300° F.) and at a pressure of about 6895kPa (1000 psig). Other process conditions may be utilized.

A hydrogenated effluent 40 from the hydrogenation zone 36 will comprisemostly saturated hydrocarbons (i.e., paraffins). The hydrogenatedeffluent 40 may be passed to a second separation zone 42. The secondseparation zone 42 may include a separator vessel or multiple separatorvessels, such as a cold separator and/or hot separator vessel (not shownin FIGURE for simplicity), and/or a column 44 or other vesselsconfigured to separate the saturated hydrocarbons. For example, in apreferred embodiment shown in the FIGURE, the column 44 in the secondseparation zone 42 separates the hydrogenated effluent 40 into a ventgas stream 46 and a saturated jet range stream 48. A portion 48 a of thesaturated jet range stream 48 may be used as a recycle stream to thehydrogenation zone 36 to be combined with the jet range olefin stream 30and hydrogen stream 34 to form a combined stream 50 passed to thehydrogenating reactor 38. The remaining portion 48 b of the saturatedjet range stream 48 comprises the desired jet-range hydrocarbons to beused as fuel or fuel blending component.

Thus, using the processes of the present invention, jet-rangehydrocarbons can be produced from a renewable olefin feedstock withminimal yield loss due to hydrogen transfer to the lighter olefins fromheavy hydrocarbons in a diluent stream.

It should be appreciated and understood by those of ordinary skill inthe art that various other components such as valves, pumps, filters,coolers, separator vessels, etc. were not shown in the drawings as it isbelieved that the specifics of same are well within the knowledge ofthose of ordinary skill in the art and a description of same is notnecessary for practicing or understating the embodiments of the presentinvention.

While at least one exemplary embodiment has been presented in theforegoing detailed description of the invention, it should beappreciated that a vast number of variations exist. It should also beappreciated that the exemplary embodiment or exemplary embodiments areonly examples, and are not intended to limit the scope, applicability,or configuration of the invention in any way. Rather, the foregoingdetailed description will provide those skilled in the art with aconvenient road map for implementing an exemplary embodiment of theinvention, it being understood that various changes may be made in thefunction and arrangement of elements described in an exemplaryembodiment without departing from the scope of the invention as setforth in the appended claims and their legal equivalents.

1. A process for producing jet range hydrocarbons comprising:oligomerizing a renewable olefin feedstock comprising C₃ to C₈ olefinsin an oligomerization reactor containing a catalyst comprising a MTTzeolite that has not been selectivated, and operating theoligomerization reactor under conditions to produce an oligomerizedeffluent; separating the oligomerized effluent to produce a lighthydrocarbon stream, a naphtha olefin hydrocarbon stream, and a heavystream comprising C₈₊ olefins; and, separating the heavy stream into jetrange olefin stream and an olefin recycle stream comprising diesel rangeolefins; and, diluting the renewable olefin feedstock with at least aportion of the olefin recycle stream.
 2. The process of claim 1 furthercomprising: blending a portion of the olefin recycle stream in a dieselblending pool.
 3. The process of claim 2 further comprising:hydrogenating the portion of the olefin recycle stream blended in thediesel blending pool before blending.
 4. The process of claim 1 furthercomprising: recycling at least a portion of the naphtha olefinhydrocarbon stream to the oligomerization reactor.
 5. The process ofclaim 1 further comprising: hydrogenating the jet range olefin stream ina hydrogenation zone having a hydrogenating reactor to provide ahydrogenated effluent.
 6. The process of claim 5 further comprising:separating the hydrogenated effluent into a vent gas stream and a jetrange hydrocarbons stream.
 7. The process of claim 6 further comprising:recycling at least a portion of the jet range hydrocarbons stream to thehydrogenation zone.
 8. A process for producing jet range hydrocarbonscomprising: passing a renewable olefin feedstock comprising C₃ to C₈olefins to an oligomerization reaction zone comprising anoligomerization reactor containing a catalyst comprising anon-selectivated MTT zeolite and wherein said oligomerization reactor isoperating under conditions to produce an oligomerized effluent; passingthe oligomerized effluent to a first separation zone to provide at leastone stream comprising C⁷⁻ hydrocarbons, a diesel range olefin recyclestream, and a jet range olefin stream; and, recycling at least a firstportion of the diesel range olefin recycle stream to the oligomerizationreaction zone.
 9. The process of claim 8 further comprising: combiningthe first portion of the diesel range olefin recycle stream with therenewable olefin feedstock to provide a combined stream; and, passingthe combined stream into the oligomerization reactor.
 10. The process ofclaim 8 further comprising: passing a second portion of the diesel rangeolefin recycle stream to a diesel blending pool.
 11. The process ofclaim 10 further comprising: hydrogenating the second portion of thediesel range olefin recycle stream before it is passed to the dieselblending pool.
 12. The process of claim 8 wherein the first separationzone produces a light hydrocarbon stream and a naphtha olefinhydrocarbon stream.
 13. The process of claim 12, wherein the firstseparation zone comprises two fractionation columns.
 14. The process ofclaim 13, wherein the first fractionation column provides the lighthydrocarbon stream, the naphtha olefin hydrocarbon stream, and whereinthe second fractionation column provides the diesel range olefin recyclestream and the jet range olefin stream.
 15. The process of claim 14further comprising: passing at least a portion of the naphtha olefinhydrocarbon stream to the oligomerization reactor.
 16. The process ofclaim 8 further comprising: passing the jet range olefin stream to ahydrogenation zone having a hydrogenating reactor containing a catalystand being operated to provide a hydrogenated effluent.
 17. The processof claim 16 further comprising: passing the hydrogenated effluent tosecond separation zone to provide a vent gas stream and a jet rangehydrocarbons stream.
 18. The process of claim 17 further comprising:passing at least a portion of the jet range hydrocarbons stream to thehydrogenating reaction zone as a recycle jet range stream.
 19. Theprocess of claim 18 further comprising: combining the recycle jet rangestream and the jet range olefin stream in a jet range combined stream;and, passing the jet range combined stream to the hydrogenating reactor.20. The process of claim 8 wherein the first separation zone comprisesat least two fractionation columns arranged in series.